Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Boiler Switch in ON position
Central Heating switch in OFF (central) position.
DHW thermostat to MAX
Gas On; Pilot On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan to run and boiler to fire.
Does the flow rate increase as the DHW temperature increases?
Is there also a 35°C rise in temperature at a flow rate of 9.8 litres/minute?